The present disclosure relates to electronics, and more specifically, to the use of radars in formulating images in accordance with one or more algorithms.
Radar may be used in connection with one or more applications. For example, a radar located on an aircraft may be used to obtain information regarding the distance of the aircraft from the ground or one or more targets or objects located on the ground. The radar may emit a signal or pulse and a scatter from a return signal may be analyzed to generate an image of a surrounding environment. For a scatter at a distance ‘R’ to the radar, the return signal may take the form:s(t)=a*p(t−τ)*ejθ(τ),where
‘a’ represents an attenuation factor associated with an emitted pulse ‘p(t)’,
‘τ’ represents a two-way delay time given by:
τ=2*R/c, where ‘c’ is representative of the speed of the emitted pulse and the return signal,
‘θ(τ)’ represents a phase term of the form −4πR/λ resulting from a delay time and center frequency of the emitted pulse, and
‘λ’ represents a wavelength of a center band or carrier frequency of the pulse.
A synthetic aperture radar (SAR) continuously emits radar pulses and collects return signals. SAR images may be generated using full aperture algorithms (FAA) and sub-aperture algorithms (SAA). When a SAR image is presented in complex form, the phase component, for most images processed using FAA, represents the two-way delay time between the averaged scatter within a pixel and the center of the full aperture. Since the location of the average scatter is very close to the pixel grid location, the major portion of this phase represents the two-way delay time between the pixel grid location and the center of the full aperture. This major phase component, however, does not exist in SAR images processed using SAA.
The lack of the phase component using SAA results in difficulty in terms of applying coherent change detection (CCD) and autofocus processes or algorithms. For example, between two repeat passes, complex images may have very different phases and may be difficult to cancel in complex form. Interference between nearby targets may make it difficult to obtain a phase error measurement.